minor typographical change to autogen added --with-html-dir option to configure more robust docbook checks convert to...

Original commit message from CVS:
* minor typographical change to autogen
* added --with-html-dir option to configure
* more robust docbook checks
* convert to standard docbook makefiles, at least for the gst/ directory
* added filesrc.h so that docbook can know about filesrc
* updated -sections.txt because docbook is incredibly stupid and requires that at
least one of the lines between <section> and </section> is not an entity
* first pass at possible getting the docs to build on glib2, untested